Typically, methods for preparing a ultra fine synthetic fiber include a direct spinning method and a conjugated spinning method.
In the direct spinning method, since a fiber is directly spun through a spinneret, it is difficult to produce a ultra fine fiber of less than 0.1 denier, and a number of problems occur in a yarn finishing and weaving step.
In contrast, in the conjugated spinning method, a two-component composite yarn is prepared by conjugated-spinning different polymers such as a polyester/polyamide composition or a polyester/copolymer polyester, and thereafter monofilaments (hereinafter, ‘fibrils’) of a fiber forming component are prepared by being separated and divided from the two-component composite yarn by a physical or chemical treatment in a post-processing process. Therefore, the method is advantageous in that it is easy to produce a ultra fine fiber of less than 0.1 denier, the fiber is easily conjugated with other fibers and the yarn finishing and weaving processability are good since fibrils are separated and divided in the post-processing process.
However, in case of solely using the two-component composite yarn, which is prepared by the conjugated spinning method, in woven or knitted fabrics, the buffability, volume property, drape property and bursting strength are reduced. Particularly, in case of conjugated spinning the polyester/copolymerized polyester composition, because the copolymerized polyester is extracted by weight reduction, a space is generated between fabric weaves and thus significantly degrading the resulting fabrics in volume property, drape property and bursting strength.
To solve the above problem occurred by solely using the ultra fine synthetic fiber or the two-component composite fiber, a method for conjugating the ultra fine synthetic fiber and other fibers has been widely studied.
As the prior art for conjugating a two-component composite fiber and other fibers, Korean Patent Laid-Open No. 1998-55564 and the same No. 1999-24801 disclose methods, as shown in FIG. 2, in which a two-component composite fiber(C) of an undrawn state is drawn and false-twisted, then is fed into an air texturing nozzle(14) at the same overfeed rate (approximately 1 to 5%) along with a high shrinkage yarn(D), and then they are simply tangled (air-interminglied) by an air pressure of 1 to 5 kgf/cm2.
In the present invention, such a interminglied yarn with different shrinkage is hereinafter defined as ‘ITY (interlaced yarn)’, which is prepared by simply interlacing a core yarn and an effect yarn in the air texturing nozzle under the condition that the core yarn and the effect yarn has the same overfeed rate of less than 5% and an air pressure is less than 5 kgf/cm2, and, as shown in FIG. 4, which consists of the core yarn and the effect yarn simply interlaced at an irregular interval along the lengthwise direction of the yarn. Specifically, as shown in FIG. 4, the ITY has a structure consisting of a compacted portion(b) and a bulky portion(C) formed alternately along the lengthwise direction of the yarn.
The interlaced yarn(ITY) with different shrinkage prepared by the above method has an advantage that it shows an excellent bulkiness due to a difference in shrinkage between the bulky ultra fine fiber and the high shrinkage yarn. And the ITY shows excellent strength and drape property due to thick monofilaments of the high shrinkage yarn used as the core yarn. However, in the above method, since an undrawn, two-component composite yarn that is weak in physical property is solely drawn and false-twisted, the process stability is significantly reduced under a common false twisting condition, and it is impossible to get a textured yarn with excellent bulkiness.
For instance, in case of drawing and false-twisting a two-component composite yarn having polyester as a fiber forming component and copolymerized polyester as an extraction component, since the thermal stability of the copolymerized polyester used as the extraction component decreases, it is inevitable to set a temperature lower than a typical heating temperature, and an enough number of false-twist (twist/unit length) cannot be given.
As the result, the prepared textured yarn with different shrinkage is greatly lowered in bulkiness, that is, crimp ratio(CR %). The crimp ratio is a representative physical property representing the bulkiness and quality of the yarn in the post-processing. Due to the lower crimp ratio, the ultra fine fiber is not sufficiently raised on the surface of the yarn, thus failing in getting the fabrics of excellent quality.
In Japanese Patent Laid-Open No. H7-126951, a method is described wherein a thermoplastic multifilament yarn (core yarn) and a low shrinkage, two-component composite yarn (effect yarn) are respectively fed into an air texturing nozzle at the same overfeed rate (approximately 1 to 5%), and then are simply interlaced (air-interminglied) by an air pressure of 1 to 5 kgf/cm2, thereby preparing a interminglied yarn(ITY) with different shrinkage.
However, the ITYs prepared by the conventional methods are different in length simply because of the difference in thermal behavior property between two yarns, so they cannot show a good suede effect in the production of woven or knitted fabrics since the dispersabilty of fibrils is lowered though the bulkiness is expressed. More specifically, as shown in FIG. 4, the interminglied yarns with different shrinkage (ITYs) prepared in the conventional methods has the shape where fibrils are simply compacted at a constant interval along the lengthwise direction of the intermingled yarn.
As a result, the concentrated fibrils are not dispersed well after producing a woven or knitted fabric, the length of raised fibers in interminglied (concentrated) portion are different from the length of raised fibers in non-interminglied (unconcentrated) portion and density of the raised fiber is irregular. By this, in the production of woven or knitted fabric, as shown in FIG. 6, raised fibers aggregate to partially expose the bottom of the woven or knitted fabric, and a superior suede effect cannot be shown.
As another conventional method, a method is widely embodied wherein a thermoplastic multifilament (core yarn) and, not a two-component composite yarn, but an ordinary low shrinkage multifilament yarn (effect yarn), are fed into an air texturing nozzle at a different overfeed rate  (approximately 5 to 50%), and then are air-textured by a high air pressure of 6 to 16 kgf/cm2, thereby preparing a textured yarn with different shrinkage.
In the present invention, such a textured yarn with different shrinkage is hereinafter defined as ‘ATY (air-textured yarn)’, which is prepared by air-texturing a core yarn and an effect yarn in the air texturing nozzle under the condition that the core yarn and the effect yarn has a different overfeed rate of 5 to 50% and an air pressure ranges from 6 to 16 kgf/cm2, and, as shown in FIG. 3, in which the effect yarn twines around the core yarn and loops(a) of the effect yarn are formed on the surface of the textured yarn.
For the thusly prepared ATY, as shown in FIG. 3, although loops are formed on the surface of the textured yarn, because the effect yarn forming the loops is not a two-component composite yarn, namely, a ultra fine fiber, the raised fiber density is low and the fibril dispersion is not occurred in the production of woven or knitted fabric, thereby failing in exhibiting a suede effect.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a textured yarn with different shrinkage (ATY) which can exhibit a superior touch and appearance in the production of woven or knitted fabric because it has a superior fibril dispersability, a high raised fiber density and a uniform raised fiber length after a buffing process.
Another object of the present invention is to provide a textured yarn with different shrinkage which shows an excellent melange effect when being dyed.
A further object of the present invention is to provide a method for preparing a textured yarn with different shrinkage which shows an excellent suede effect.